Red and Grey squirrels cannot co-exist for a number of reasons.
The main reason for this is that grey squirrel carries a disease called Squirrelpox virus (SQPV). This is carried by grey squirrels, which show no symptoms, and in some circumstances is passed to red squirrels when the two species come into contact. It is estimated that the loss of red squirrels in Britain has happened 20 times faster than it would have done had squirrel pox not been a factor.

The second reason for the loss of red squirrels is a result of the competitiveness of grey squirrels. The grey squirrel is larger than the red squirrel, weighing approximately twice that of a red squirrel at 600 grams.

Finally, the grey squirrel also has a behavioural advantage. Unlike the red squirrel, which is primarily arboreal and spends approximately one third of its time on the ground, the grey squirrel spends more than three quarters of its time foraging on the woodland floor. This adaptation means that, in the autumn, grey squirrels can increase their body weight by as much as 20% while reds, which feed far less efficiently in broadleaved woodland, rarely manage to gain 10%.

As a result of the invasive behaviour of the grey squirrel and the subsequent loss of red squirrels it has now been listed within a list of the 100 worst invasive species globally by the IUCN.

In addition the grey squirrel has been included as a key species for action in a new EU regulation on Invasive Alien Species. The regulation focuses on the effective and coordinated management of Alien Invasives, and entered force on the 1st January 2015.

In order for the re-introduction to take place it is essential we not only remove grey squirrels from the two target areas but demonstrate that future reinvasion by grey squirrels can be precluded. The primary method for this is live trapping, meaning that any non-target animal caught by mistake can be released unharmed. Traps are checked at least every 24 hours and grey squirrel culling is carried out following legislative and best practice guidance, including the Forestry Commission paper on grey squirrel control.You can read the detailed strategy document for CRSP here, which explains how we propose to the remove grey squirrels from the two target areas.

This approach is the same as that undertaken successfully on Anglesey, which led to the re-colonisation of the island by native red squirrels, and is employed in the north of England and Scotland as a grey control method.